1. Field of the Invention
This invention relates to liquid pumping means for thermal management systems and, in particular, to a method of thermally pumping a volatile fluid and to a capillary check valve pump used in the method.
2. Description of the Prior Art
In current space activities, the very large, long-life space systems presently being planned are based on the large lift capabilities of the United States Space Shuttle. These large satellites and other space projects will require thermal management systems with multikilowatt capacity capable of collecting and transporting heat from various subsystems to heat rejection radiators. Transport distances are expected to be on the order of 10 to 30 meters. Current technology for large thermal transport systems is based on circulating liquid loops. These tend to be heavy and vulnerable to micrometeroid puncture, have relatively low thermal performance (film coefficients), and require significant amounts of pump power. As current demonstrated pump life is only 21/2 years, the pumps and the required valves also lower system reliability. Many problems inherent in thermal systems using a circulating liquid can be alleviated by using a capillary-pumped two-phase circulating system. Liquid delivered to the mounting panels on which heat generating equipment is fixed would pick up heat by evaporation. The vapor would be delivered to heat sinks, yielding heat by condensation. Compared to circulating liquid systems, mass flow rates and liquid line sizes would be reduced, film coefficients would be higher, and pump power would be reduced.
Although a two-phase wick-type heat transfer system using heat pipe principles avoids the requirement for mechanical pumps with their attendant disadvantages because of their moving parts and the like, it is sometimes desirable to provide more precise thermal control over the system and also to improve its heat transport capacity. In addition, in some two-phase systems under stated circumstances, it is advantageous to keep certain fluid lines open continuously if such can be arranged without the use of a solenoid valve. The pumping method and the capillary check valve pump of the present invention serves these desired functions.
In the prior art, apparatus with no moving parts in which a liquid is heated to produce a vapor that can be used for pumping functions is disclosured by E. A. Weaver (U.S. Pat. No. 1,847,286); S. H. Raskin (U.S. Pat. No. 2,763,246); B. D. Power (U.S. Pat. No. 3,686,474); B. D. Power et al. (U.S. Pat. No. 3,781,518); H-L. von Cube (U.S. Pat. No. 3,817,321); and J. F. Pollock et al (U.S. Pat. No. 3,943,330). Weaver, Power, Power et al., and Pollock et al. use the capillary action of a porous membrane as the liquid feed means in their pumps. Vaporization is enhanced by heating the membrane, either by the Joule Effect, or in the case of Weaver, by a heat input into the vaporization surface of the membrane. Raskin discloses a device which is not a pump per se but a construction which uses a heat input into a column of liquid to generate bubbles therein, which bubbles are conveyed to an outlet such that intermittent puffs of steam are produced. Unlike the present invention in which a liquid is pumped, the output of the aforementioned references except von Cube, is a vapor. In von Cube, a "bubble pump" using a heat input from electronic equipment cooled thereby is used to circulate the liquid employed in cooling. Although means for pumping a liquid is disclosed by von Cube, the capillary means for pumping and flow control of the present invention is not used in his apparatus. There are also showings in L. V. Lucia (U.S. Pat. No. 1,922,546); C. J. Van Hook (U.S. Pat. No. 2,755,792); and J. D. Buchanan et al. (U.S. Pat. No. 3,065,712) of pumping means in which a vapor is used to pump a liquid. In those prior art showings, a liquid in a chamber is heated to produce a vapor that pumps liquid from the chamber. Unlike the present invention which teaches a liquid pumping method and a pumping means with no moving parts for use therewith, the latter-referenced references teach means which require the use of mechanical check valves for their operation.